Vaccine for the H7N9 Bird Flu: How Will We Know It Works?

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Although the rise in cases of the H7N9 bird flu in China seems to
have slowed, health officials are developing a vaccine against
the virus, and will test it in a clinical trial, experts say.

But how will they know the vaccine works?

The first step is to make a vaccine. Researchers at the Centers
for Disease Control and Prevention (CDC) have already made a
preliminary " seed
vaccine" against strains of the H7N9 virus that have been
found in infected people. Earlier this month, the CDC offered to
begin shipping this vaccine to manufacturers that wanted to start
creating batches to be used in testing.

Next, volunteers in the United States will be recruited for the
trial, said Dr. Anthony Fauci, director of the National Institute
of Allergy and Infectious Diseases. During the trial, health
officials will assess the vaccine's safety (such as whether there
are any adverse reactions).

They will also look at the strength of immune response the
vaccine induces in people, to see whether the vaccine could
successfully protect a person against infection, Fauci said. The
NIH will oversee these trials.

There has been some concern that a
vaccine against H7N9 might not induce an immune response
strong enough to be effective. Studies of vaccines against
viruses in the H7 family have suggested that even two vaccine
doses do not produce an adequate response, Michael Osterholm,
director of the University of Minnesota's Center for Infectious
Diseases Research and Policy, wrote in an editorial in the
Journal of the American Medical Association on May 9.

Some vaccines contain ingredients called adjuvants, which boost
their effects. Although adjuvants have not been added to flu
vaccines in the United States in the past, the clinical trials of
the H7N9 vaccine will include one version with an adjuvant, and
one without, Faucitold LiveScience.

Because no cases of H7N9 have been reported in the United States
— and because it would be unethical to expose people to the virus
just to test the vaccine — the trials cannot directly assess the
effectiveness of the vaccine in preventing H7N9 infection.

However, researchers will indirectly test the vaccine's
effectiveness by taking blood from vaccinated people, and
checking to see if antibodies in their blood can neutralize (or
kill) the
H7N9 virus in lab dishes, Faucisaid.

Similar trials have been conducted in the past for the H5N1
vaccine, Fauci said.

Health officials are not yet sure whether they will need to use
the H7N9 vaccine. The decision to produce large quantities of the
vaccine and vaccinate the public will depend on whether H7N9
turns into a global disease outbreak, Faucisaid.

Right now, cases of H7N9 have not been seen outside China and
Taiwan, and there have been no reports of sustained
human-to-human transmission of the virus. As of May 8, health
officials knew of 131 people who had been infected with H7N9, of
whom 32 had died, according to the World Health Organization.